Risk Premium Investing A Tale of Two Tails

Transcription

1 Risk Premium Investing A Tale of Two Tails Executive Summary In this note we introduce Risk Premia as generically encompassing a set of strategies where investors are compensated for assuming risk. This compensation comes in the form of a regularly received premium and results in a strategy with a positive expected return. This positive performance continues until the moment the risk, which is being assumed, is realized, resulting in a sharp negative move. The argument generally invoked is that this premium is proportional to the risk or volatility of the investment or instrument being held, a measure which uses both sides of the return distribution. In this paper we expand on the idea of a risk premium, with the help of a few example strategies, and show that the premium is in fact compensation for downside deviation or negative skewness risk, an idea which is justified with empirical evidence and also appeals to common sense. Introduction Presented with two investments of equal expected return, a rational investor will choose the one with the lowest risk. This statement can also be turned around as, given two investments offering differing levels of risk, the higher risk investment needs to provide a higher level of excess return in order to entice people in to invest. Within the Efficient Market Hypothesis (EMH), excess returns are only possible due to the existence of a risk premium. In fact EMH proponents will often explain away positive excess returns as being due to the existence of some form of hidden or latent risk. This risk, in financial parlance, is generally represented as the standard deviation (although sometimes other measures are used) of a time-series of returns. These standard measures of risk use both sides of the return distribution and do not distinguish up moves from down moves. The existence of a risk premium as being compensation for assuming a volatile position makes sense. However, the idea does not satisfactorily account for investments exhibiting negatively skewed, asymmetric return streams. We instead, therefore, propose that a risk premium represents compensation for an investment that has a non-zero probability of selling-off sharply and we use the following example to illustrate our point. A short position in VIX futures is a profitable trade over a long back-test. At the onset of any crisis, however, experience tells us that it is a strategy that can have significant downside risk. A long position in VIX futures, though, has an equal amount of two sided risk or volatility to a short position, but with the opposite return profile. Are we to believe that a long position and a short position in VIX futures should have the same amount of risk premium? Clearly not and there is, therefore, a sign ambiguity which is resolved by considering risk premium as compensation for downside risk. So, what does downside risk mean for a strategy? If we were to plot out the performance of a stream of returns with higher downside risk than upside risk we may see something like the curve plotted in Figure 1. We have also plotted a zero skewness (symmetric) strategy and a positively skewed (upside risk higher than downside risk) strategy for comparison. The negatively skewed investment is characterized by having frequent small positive returns and infrequent large negative returns. Figure 1 also shows the cross sectional profile of the returns of the strategies showing the differences between the three regimes. Any investor, given the choice between these return profiles, will prefer a positive Sharpe/positive skewness strategy and it is this bias against negatively skewed strategies that creates the risk premium. In this note we present our approach to improving the skewness profile of a risk premium offering through both diversification and the power of the combination with non-risk premium, behavioral anomaly strategies such as trend following. 1

2 Skewness=0 Positive skewness Negative skewness Figure 1: Three strategies with different skewness profiles (negatively skewed, zero skewed and positively skewed). The superimposed plot shows the cross sectional profile of the corresponding returns. Insurance a classic example of a risk premium strategy Insurance policies cover a multitude of outcomes from the theft of a car or a house burning down, to a professional footballer's capacity to play football. Most people are familiar with the concept of insurance, but less so with how insurance companies generate profit. Within an insurance company, actuaries attempt to evaluate the probability of an insured outcome occurring, and subsequently calculate a fair value for a given policy. A mark-up is applied to the cost of the policy representing the premium charged to the end client such that on average a profit is generated. The return profile for the insurance company is, therefore, a stream of positive payments from the premiums received and an occasional large negative move when the insured outcome actually occurs and requires a pay-out. An insurance company will not just rely on one policy to run its business, diversification is essential to the model in reducing the negative skewness profile of the returns and improving the comfort level of the company's shareholders. It is this decorrelation between the pay-outs that is crucial to reducing the downside risk of the firm, a point we will address below. A concern of any insurance firm shareholder will be the potential for a non-diversifiable component of risk. For example, let's say that an insurance company has sold policies insuring houses across a country or continent. Let's also say, for the sake of argument, that a natural disaster occurs - a meteor destroying a large industrial area, or flooding that destroys homes and factories, or an earthquake, a tsunami etc... It is the existence of these correlated events requiring an instantaneous profusion of pay-outs across many clients that represents an incompressible risk for the insurance firm. This risk has been addressed more recently with the introduction of catastrophe bonds to the market place. A hedge fund or pension fund may decide to offer the insurers insurance against these types of correlated pay-outs, but of course this insurance comes at a price! 1 We discuss the idea of incompressible risk in a financial context below. 1 Insurers may also invoke exceptional Act of God clauses in insurance contracts to avoid this risk 2

3 A few examples of Risk Premia (and others that are not) We begin with some familiar examples of risk premia from the world of traditional asset classes and investments. Holding equities is a well-known strategy and is often a big component of investor portfolios. Although the skewness of individual equities is quite small, when combining stocks together to form an index, the skewness becomes negative. This leverage effect is well known, and is due to the fact that stocks tend to correlate in their downward moves, creating the negative fat tail for the index, and thus making long-only equities a risk premium strategy. Experience of stock markets tells us that they tend to drift upwards over long periods, albeit with weak Sharpe ratios, but can sell-off sharply. One can see the measured Sharpe ratio and skewness 2 in Table 1, showing that equity indices are our first example of a risk premium strategy. Instruments/Strategies Skewness Sharpe ratio S&P DAX Nikkei year US government bond year US government bond year German government bond year German government bond Corporate bond index (US B rated) Short equity index volatility Short 10 year bond volatility Short energy volatility Short metal volatility Short grain volatility Short FX volatility UMD US HML US Trend following Table 1: Skewness and Sharpe ratios for a set of instruments and strategies. Of perhaps more interest for this note is another traditional asset class - that of fixed income. Short dated government paper, issued by the most creditworthy governments such as the US and Germany 3, exhibits positively skewed returns due to the safe haven nature of the investment. In periods of risk-off and flight-toquality, investors seek to hold these types of investments, even more so than cash (which necessarily involves being exposed to a potentially uncreditworthy bank!). The post 2008 climate of extreme, loose monetary policy has, however, pushed rates to record lows and investors to seek other sources of return. Indeed it is precisely 2 We use the non-parametric skewness as defined by en.wikipedia.org/wiki/skewness. This is a more stable measure than the third moment, a point which is discussed in [1]. 3 One may argue that Germany is now less creditworthy due to the fact it no longer controls its own money supply and can therefore not just print cash to pay off its debts 3

4 for this reason that central banks employ such policies! A portfolio manager may, therefore, turn to the world of corporate bonds to try to get an extra pick-up on his cash, with corporates needing to offer a higher level of return compared to a government in order to entice investors to buy their debt. Of course, the investor is fully aware of the fact that if things don't go well for the firm then the bond principal is at risk and may not be repaid. However, intuition is strong that this risk can be diversified away (we will describe this more quantitatively later) by buying a basket of corporate bonds offering a wide ranging mix of corporate debt. This approach allows the investor to diversify away a lot of their credit risk, whilst benefiting from the pick-up in yield versus government bonds. The investor may be exposed to a non-diversifiable risk that defaults correlate across firms. It is for this reason that an investment in a diversified basket of corporate debt will yield more than government paper, as compensation for the existence of this correlated default risk. In Table 1 we summarize the case of US short dated government paper exhibiting a positive skewness meaning it is not a risk premium strategy, while longer dated government bonds and, certainly, corporate bonds stand-out as clear risk premium strategies. Insurance selling in finance comes from the options market. If a big pension fund is holding a large equity portfolio and is fearful of adverse moves due to an upcoming FOMC, the pension fund may choose to protect its portfolio by buying down strike put options. In so doing, the investor is pushing option prices up, implied volatility up relative to realized volatility, and paying a premium to the option seller. The option seller is providing protection and so requires a premium for taking on the risk that the hedger wants to offload. If nothing happens through the FOMC then the option seller has made money by receiving a high price for the insurance. If, however, the move that the investor feared actually comes to fruition then the option seller faces a potentially large pay-out. This risk can again be mitigated and the negative skewness reduced by diversifying over many different options on many different underlyings. When applied to this example, the idea of non-diversifiable or incompressible risk that we touched upon earlier corresponds to a volatility move that correlates across underlyings. In the biggest financial crises one observes that this is indeed the case, with losses being seen across asset classes. We do, however, see an improvement in the negative skew and Sharpe ratio characteristics from a short volatility portfolio that is diversified across many underlyings, which suggests that we are more able to diversify away this risk than one might imagine. At the beginning of the 1990s, Eugene Fama and Kenneth French identified certain market neutral portfolios in the US stock market that seemed to exhibit positive excess returns. Here we focus on two Fama and French factors UMD 4 and HML. UMD refers to Up Minus Down as being a market neutral portfolio of the trend applied to individual stocks, exploiting the fact that outperforming stocks tend to continue to outperform while underperforming stocks continue to underperform. Measuring the skew of this strategy shows that the factor exhibits negative skewness. What is interesting, however, is that the large downside moves come from upside moves in the index. Despite the fact, therefore, that the strategy has negative skewness, it is a true diversifier in the sense that the negative skewness comes from risk-on environments occurring at times unrelated to the drawdowns of other risk premium strategies. Let us now switch our attention to the HML factor. HML refers to High Minus Low, a market neutral factor that is long stocks that have a high book value 5 to price ratio and short stocks that have a low book to price ratio. The strategy is a classic value strategy in that one exploits the fact that prices should move in tandem with a fundamental value metric such as book value. We find in this case that HML exhibits a positive skewness. A positive Sharpe ratio strategy with positive skewness is rare indeed. Our claim in this short note is that positively skewed, positive Sharpe ratio strategies do not come from the family of risk premia, but rather generate returns by exploiting some form of market anomaly. The case of the HML factor is curious, however, and not easily explained. The skewness of the strategy turns negative when using monthly data, adding to the 4 UMD was not one of the original Fama French factors but was introduced in subsequent factor literature 5 Book value is assets minus liabilities. In the absence of earnings it is a good starting point for valuing a company 4

5 confusion, and necessitating further work. Table 1 summarizes the statistics for the two Fama French factors using stocks across a range of geographical zones. The final example we will discuss here is another case of a strategy exhibiting positive skewness. Trend following is a special case due to its relationship with risk, as has been discussed in our paper on the subject [2]. Trend following will perform in times of market stress if the difficult period persists for a time comparable to, and ideally longer than, the timescale over which one trends. That being the case, a classic trend following system will short crashing equities and other risk sensitive instruments and will buy bonds and other flight-toquality instruments. As long as the crisis period persists for longer than the trend timescale, there is a guaranteed payoff. This long volatility component of trend following is what gives us a positive skew and was the reason for its success through the 2008 global financial crisis. We would argue that the trend is in fact not a risk premium strategy, but rather a genuine market anomaly arising out of the extrapolative tendencies of investors. Many other examples of strategies have been studied and we invite interested readers to consult [3] for a more comprehensive list and description. Is Risk Premium compensation for high volatility or negative skewness? We have presented our understanding of risk premium strategies as having positive Sharpe ratios and negative skewness, with the positive excess returns being the reward for assuming downside risk. This idea appeals to common sense, but can we show this to be the case empirically? CFM has done research on this subject [3] which culminated in the plot seen in Figure 2. We took as many standard, well-known, accessible strategies as we could, many of which are discussed in the previous section, and plotted the Sharpe ratio against the level of skewness. One sees a cloud of points that are dispersed around an explanatory line, suggesting that indeed, the higher the reward or Sharpe ratio, the higher the level of negative skewness. The suggestion is, therefore, that strategies that lie below the line have too much negative skewness compared to the level of excess return while, contrarily, strategies above the line have too much excess return for the level of negative skewness. This is indeed the case for the two strategies discussed above - trend following and the HML equity market neutral factor. One observes that both have positive excess returns with a positively skewed return distribution and, for this reason, our conjecture is that, rather than these strategies being Risk Premia, they instead represent genuine market anomalies. 5 Figure 2: The skewness rewarding line showing a quasi-linear relationship between the Sharpe ratio (the reward) and the negative Skewness (the risk), for a set of strategies and instruments.

6 An interesting question is now whether volatility (the standard deviation of returns) has the same explanatory power. What we see in [3] is that volatility surprisingly tends to do the opposite of skewness in that the low volatility strategies systematically outperform those with high volatility, a result which is at odds with an explanation of a risk premium being due to volatility. This fact also explains the low vol effect [4], a recent hot topic in the academic community. Interpreting risk premium, therefore, as compensation for downside risk rather than symmetric risk seems to be consistent with the data. Classifying and diversifying negative skewness strategies As previously stated, we are putting forward the idea that a premium exists for holding a negatively skewed investment. The origin of this negative skewness can, however, be different across a range of strategies. Identifying the nature of the risk premium is important when trying to combine strategies together to produce a higher Sharpe ratio and overall better skewness profile (ideally making it positive). Combining negatively skewed strategies together should reduce the overall negative skewness of the combination. In order to illustrate our point, we have taken a number of negatively skewed strategies which can be seen in Figure 3. Before we combine them together, it is crucial to note that the skewness is not correlated across the strategies, meaning that the down moves do not typically arrive together, simultaneously, across the strategies. We have superposed the combination of these de-coskewed strategies on the same plot, and show that both the Sharpe ratio is improved and the level of negative skewness reduced. If we continue adding strategies then the Sharpe ratio will continue to rise and the skewness will fall to zero, meaning we end up with a symmetric return distribution. As discussed above, this is in the absence of non-diversifiable risk which may materialize itself as a correlation of downward moves across all strategies and an increase in negative skewness, something we are trying to avoid Negatively skewed P&L s Combination of the 5 P&Ls Figure 3: An illustration of the effect of diversification on skewness. The combination of a set of de-coskewed strategies with negative skews results in a combined strategy with better Sharpe ratio and close to zero skewness. The figure is based on simulated data and is for illustration purposes. We listed several classic, well known strategies in the previous section. The question is when, on average at least, is a strategy more likely to sell-off? If the strategy expresses its risk with a sharp sell-off in a rising market, such as the UMD Fama-French factor, then we consider the strategy to be risk-on premium whereas if the strategy sells off during a down market, such as a short option strategy, then we are receiving a risk-off premium. Catastrophe bond buyers, on the other hand, take on catastrophe risk premium which would incur 6

7 losses following a natural disaster, which may or may not be correlated with a risk-off move (depending how big the catastrophe is!). Liquidity providers, on the other hand, may be seen as assuming a liquidity risk premium, the risk being that they are executed and lose money on large price jumps, in either direction, in the instrument they are providing liquidity for. Identifying many different types of risk premia and allocating to them should, we believe, help to reduce the forward looking negative skewness of a risk premium portfolio. The special case of trend following, which we are claiming to be a behavioral anomaly, is also useful in combination with risk premium strategies. We deal with this case below. It is interesting to note that the HFRX hedge fund index sits close to the negative skew/sharpe ratio reward line, as seen in Figure 2, albeit sitting slightly below it. We also show in the plot, the effect of correcting hedge fund returns for fees, showing that the point then moves up to sit on the line. This is interesting and may suggest that hedge funds are exploiting risk premia in their strategies. Anecdotally, this seems consistent with a poor overall performance through the global financial crisis of 2008 when hedge funds lost a significant proportion of their assets. Although we see value in a well implemented risk premium portfolio, the advent of Alternative Beta offerings may drive fees down and the HFRX point up closer to the line. We would also like to bring the reader's attention to the Diversified Risk Premia point in Figure 2, where we combine a portfolio of equity indices, a diversified portfolio of short options, an FX carry strategy and long the four CDS indices in the US and Europe. This point sits satisfactorily above the regression line and represents a diversified risk premium portfolio. It seems, therefore, that one is able to improve the Sharpe ratio/negative skewness characteristics of risk premium investing through diversification. The idea of non-diversifiable or incompressible risk, that we alluded to earlier in this paper, does not preclude us from improving the characteristics of the investment and, therefore, we favor this approach in building our portfolio. We have studied the possible existence of this incompressible, or Black Swan risk, by attempting to identify the factors of the combination of all risk premium strategies that went into Figure 2. A dominant market factor does not seem to exist, however, unlike the case of the market mode for a portfolio of stocks. Instead, two poorly separated and unstable factors emerge, suggesting the absence of a clear benchmark for risk premium investing. The idea of incompressible risk, nevertheless, seems plausible and we favor an approach of attempting to mitigate this risk, as previously stated, by combining and diversifying different sources of risk premia. A tail hedge with the trend Trend following, both empirically and intuitively, does not exhibit a negative skewness and, as such, we consider it a market anomaly rather than a risk premium strategy. The positive skewness properties of trend following make it a good strategy in combination with risk premia, in particular with strategies which perform poorly in times of market stress. We take, as an example of the latter, a diversified short volatility strategy that is short options on interest rates, equity indices, commodities and FX and is plotted in Figure 4. In Table 2 we list the worst performing months of this strategy, along with the corresponding performance of a trend following system. What is striking is that for 6 out of 8 periods of the worst performance for our short volatility premium strategy, trend following delivers positive performance. This anti-correlation in the tails of these two strategies provides a form of statistical downside protection to the risk premium approach. The two strategies are combined together in Figure 4, showing the benefits of a skewness diversified approach. 7

8 Start date End date Diversified Short Volatility (%) Trend Following (%) Aug-08 Nov Oct-87 Nov Jul-90 Sep Jul-14 Jan Oct-97 Nov Mar-13 Jun Apr-10 Jun May-07 Sep Table 2: The worst performing periods for a diversified short volatility strategy and the corresponding performance of a 50 day trend following strategy in the same period day Trend Following Diversified Short Volatility Combination Jan Jan-87 Jan-91 Jan-95 Jan-99 Jan-03 Jan-07 Jan-11 Jan-15 Figure 4: The performance of a diversified 50 day trend following strategy, a diversified short volatility strategy and an equally weighted combination of both. The improvement in Sharpe and in drawdown depth is clear in the combination. 8

9 Conclusions Risk premium is compensation for assuming downside risk, and negative skewness seems to be a better explainer of the premium than volatility. If anything, there seems to be a premium for holding low volatility instruments and this is the basis of the much discussed low volatility effect. Negative skewness can be reduced in a portfolio by combining many de-coskewed strategies, and the skewness profile of risk premium investing improved further in combination with a trend following strategy. We believe that this approach is what all good Alternative Beta investment managers should strive to achieve. References [1] Errors on Statistical Measurements in Finance. P. Seager, forthcoming. [2] Two Centuries of Trend Following. Y. Lempérière, C. Deremble, P. Seager, M. Potters, J.P. Bouchaud. 2014, Journal of Investment Strategies [3] Tail Risk Premiums versus Pure Alpha. Y. Lempérière, C. Deremble, T. T. Nguyen, P. Seager, M. Potters, J.P. Bouchaud. 2015, Risk Magazine. [4] Deconstructing the Low-Vol Anomaly. S. Ciliberti, Y. Lempérière, A. Beveratos, G. Simon, L. Laloux, M. Potters, J. P. Bouchaud

10 Important Disclosures ANY DESCRIPTION OR INFORMATION INVOLVING INVESTMENT PROCESS OR ALLOCATIONS IS PROVIDED FOR ILLUSTRATIONS PURPOSES ONLY. ANY STATEMENTS REGARDING CORRELATIONS OR MODES OR OTHER SIMILAR STATEMENTS CONSTITUTE ONLY SUBJECTIVE VIEWS, ARE BASED UPON EXPECTATIONS OR BELIEFS, SHOULD NOT BE RELIED ON, ARE SUBJECT TO CHANGE DUE TO A VARIETY OF FACTORS, INCLUDING FLUCTUATING MARKET CONDITIONS, AND INVOLVE INHERENT RISKS AND UNCERTAINTIES, BOTH GENERAL AND SPECIFIC, MANY OF WHICH CANNOT BE PREDICTED OR QUANTIFIED AND ARE BEYOND CFM'S CONTROL. FUTURE EVIDENCE AND ACTUAL RESULTS COULD DIFFER MATERIALLY FROM THOSE SET FORTH, CONTEMPLATED BY OR UNDERLYING THESE STATEMENTS. 10